1. Field of the Invention
The present invention relates generally to a method of accounting for angle-dependent wavelet stretch in seismic data. More particularly, the invention relates to a method of accounting for angle-dependent wavelet stretch in seismic data based on a novel relationship between wavelet stretch and a reflection angle of an acoustic ray.
2. Description of the Prior Art
The use of seismic surveys is now fundamental in the search for oil and gas reservoirs in the earth. Seismic surveys, including seismic reflection surveys, are typically performed by imparting acoustic energy of a known amplitude and frequency pattern at one or more locations of the earth (either at a land surface or in a marine environment) and then detecting reflected and refracted acoustic energy at other locations. The time delay between the imparting of the acoustic energy at the source location and the detection of the same wave at a receiver location is indicative of the depth at which a particular reflecting geological interface is located. The field of seismic data interpretation is concerned with techniques for analyzing the detected seismic waves to determine both the location and the properties of various geological strata.
As is known in the art, common depth point and other conventional seismic survey approaches utilize a plurality of source and receiver pairs to emit and detect acoustic energy or rays. However, due to the physical offset between different source and receiver pairs, acoustic energy or rays are detected at different times by the plurality of receivers. Thus, traces and wavelets resulting from conventional seismic survey approaches are often subject to shifting, known as normal move-out, caused by the physical offset between different source and receiver pairs.
Conventional and well-known methods, commonly referred to as normal move out correction, have long been employed to correct for normal-move out and its undesirable effects. However, normal move out correction, and other prestack processes such as time migration and depth migration, stretch wavelets as a function of angle. This angle-dependent stretching of the wavelet, commonly referred to as normal move-out stretch or angle-dependent wavelet stretch, results in the undesirable loss of high frequency data at far offset. The wavelet stretch flattens out the peaks of the wavelets, thereby extending the time length of each pulse over a wider range than an unstretched wavelet, resulting in energy bleeding. Such distortion or stretch is obviously undesirable, as it results in the loss of data which may be required or useful for additional analysis.
Various methods of accounting for angle-dependent wavelet stretch exist. However, these methods are generally unduly complex and require extensive calculations or modeling of data. As a result of this complexity, prior art methods of accounting for angle-dependent wavelet stretch generally require a great expenditure of human time and/or computing time, thereby preventing widespread use of the prior art methods. Furthermore, such complex and extensive calculations may not be easily included or implemented in existing methods or computer programs, thereby further inhibiting use of the prior art methods.
Additionally, prior art methods of accounting for wavelet stretch generally are unable to account for wavelet stretch in more than one situation. For instance, prior art methods which are operable to correct angle-dependent wavelet stretch in normal move out corrected data may not be operable to forward model wavelet stretch on seismic data. Similarly, prior methods for forward modeling wavelet stretch on seismic data may not be operable to correct for angle-dependent wavelet stretch, etc.